The invention relates to fuel additives and to processes for making the fuel additives which additives provide octane enhancing performance without significant environmental consequences.
Fuels, particularly gasoline grade fuels have undergone many changes over the years in order to improve engine performance and reduce engine emissions. Many octane improving compounds used for improving engine performance and extending fuel supplies, such as tetraethyl lead, aromatic compounds, methylcyclopentadienyl manganese tricarbonyl, methyl tertiary butyl ether (MTBE) and other such additives, have fallen into disfavor because of concerns about adverse environmental consequences arising from their use. Accordingly, there is a need for improved fuel additives which provide enhanced engine performance and can be used to extend fuel supplies without adversely affecting the environment.
With regard to the foregoing, the invention provides a fuel additive composition including from about 85 to about 99% by volume C1-C4 alcohol having a first blending octane number and from about 1.0 to about 15% by volume of a compound selected from the group consisting of dialkoxyalkanes, alkoxyalcohols, trialkoxyalkanes, dialkoxycycloalkanes and aryl alkyl diethers having a second blending octane number and a boiling point in the gasoline boiling range. The resulting composition has a third blending octane number which is substantially greater than a linear addition of the first and second blending octane numbers of the components of the mixture. In the composition, the second blending octane number is substantially lower than the first blending octane number.
In another aspect the invention provides a method for making a fuel additive composition. The method includes heating a C1-C4 alcohol in the presence of a neutral or basic platinum catalyst to a temperature and pressure sufficient to produce an additive composition containing from about 85 to about 99% by volume C1-C4 alcohol having a first blending octane number and from about 1.0 to about 15% by volume of a compound selected from the group consisting of dialkoxyalkanes, alkoxyalcohols, trialkoxyalkanes, dialkoxycycloalkanes and aryl alkyl diethers having a second blending octane number and a boiling point in the gasoline boiling range, wherein the alcohol is heated in the substantial absence of aldehydes or ketones. In the composition, the second blending octane number is substantially lower than the first blending octane number.
In yet another aspect the invention provides a method for increasing the octane number of a gasoline fuel. According to the method, from about 85 to about 95% by volume gasoline fuel having a base octane number is mixed with from about 5 to about 15% by volume fuel additive composition including a C1-C4 alcohol containing a minor amount of an ether compound selected from the group consisting of dialkoxyalkanes, alkoxyalcohols, trialkoxyalkanes, dialkoxycycloalkanes and aryl alkyl diethers having a boiling point in the gasoline boiling range, wherein the amount of ether compound in the alcohol additive composition is sufficient to increase a blending octane number of the gasoline fuel an amount ranging from about 4 to about 15% over the base octane number of the gasoline fuel.
The fuel additive composition as described above provides what is believed to be a synergistic increase in octane number of the additive composition and fuel over what would be expected based on the octane number of the components. For the purposes of this invention, the octane number is defined as (R+M)/2 wherein R is the research octane number and M is the motor octane number. The synergistic increase in octane number was totally unexpected.
An important aspect of the invention is the use of a relatively low molecular weight ether compound in combination with a C1-C4 alcohol to provide a fuel additive having octane improving characteristics for use in gasoline fuels. The relatively low molecular weight compound is selected from the group consisting of dialkoxyalkanes, alkoxyalcohols, trialkoxyalkanes, dialkoxycycloalkanes and aryl alkyl diethers having a second blending octane number and a boiling point in the gasoline boiling range.
Preferred dialkoxyalkanes having the desired characteristics include, but are not limited to, 1,1-diethoxyethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, and 1,2-diethoxyethane and the like. The alkoxyalcohols may be selected from 2-ethoxyethanol and 2-(2-methoxyethoxy)ethanol and the like. Trialkoxyalkanes which may be used include 1,1,1-trimethoxypentane, 2-ethoxyethyl ether and 2-methoxyethyl ether and the like. A preferred dialkoxycycloalkane includes 1,1-dimethoxycyclohexane and the like. The aryl alkyl ethers may be selected from 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, 2,3-dimethoxytoluene, 3,5-dimethoxytoluene and the like.
A particularly preferred ether compound is a di- or tri-alkoxy alkane, most preferably a compound of the formula
R1xe2x80x94CH(OR2)x
wherein R1 is selected from the group consisting of a hydrogen atom and an alkyl group containing from about 1 or 4 carbon atoms, R2 is selected from the group consisting of methyl and ethyl groups and x is an integer selected from 2 and 3. Of the ether compounds 1,1-diethoxyethane (acetal) and 1,1,1-trimethoxypentane are the most preferred. Ether compounds of the foregoing formula are conventionally formed by reacting aldehydes or ketones with an excess of alcohol in the presence of trace mineral acid. The formation of acetal under these conditions is an equilibrium process. That is, acetal in the presence of water and acid react to form alcohol and aldehyde.
In contrast to conventional processes for forming acetals, a unique process is provided which not only produces acetals, but provides an additive composition having desirable octane enhancing qualities. According to the process, a relatively pure C1-C4 alcohol, most preferably ethanol, is heated in a reaction vessel in the presence of a catalyst at a temperature and pressure sufficient to form a mixture containing from about 1.0 to about 15% by volume acetal and from about 85 to about 99% by volume C1-C4 alcohol. Trace amounts of water may be present in the alcohol. The term xe2x80x9crelatively purexe2x80x9d means that the alcohol used as a reactant is from about 95% by volume to about 100% by volume alcohol.
The catalyst is selected from noble metal catalysts such as palladium, gold, silver, ruthenium, rhodium, iridium and platinum and is preferably platinum. The platinum catalyst may be supported or unsupported. If supported, it is preferred that the catalyst support be a neutral or basic catalyst support such as neutral or basic aluminum oxide. The amount of catalyst present on a supported catalyst may range from about 0. 15 to about 0.45% by weight catalyst per weight of support material.
The reaction is preferably conducted at a temperature ranging from about 120xc2x0 to about 210xc2x0 C. and at a pressure ranging from about 350 to about 650 psia. The reaction is conducted for a period of time sufficient to increase the amount of ether compound in the alcohol to the desired amount. A preferred amount of ether compound in the alcohol product ranges from about 1.0 to about 15% by volume based on the total volume of reaction product. A particular preferred reaction product contains from about 2 to about 10% by volume acetal or 1,1,1-trimethoxypentane and from about 90 to about 98% by volume alcohol.
The reaction may be conducted continuously or in a batch or semi-batch process. Since the reaction time at elevated temperatures is relatively fast, relatively small reaction vessels are needed to provide the additive compositions as claimed. Depending on the scale of the reaction, reaction times may vary from 30 minutes to 3 hours or more using volumetric space velocities ranging from about 3.0 to about 15.0 feed vol./catalyst vol.